1. Describe the overall plan of the alimentary canal.
1) esophagus- transport
2) stomach- mechanical disruption , absorption of water and alcohol
3) small intestine – chemical and mechanical digestion / absorption.
4) large intestine – absorb electrolytes (salts and water) and vitamins
5) rectum and anus – defecation
2. Describe the features of each layer of the alimentary canal.
1) Mucosa: 3 layers are always present in GI tube with varying thickness
epithelium
lamina propria- CT
muscularis mucosae – thin layer of muscle
2) Submucosa: contains vessels, some nerves. Contains glands in 2 regions of GI (esophagus and duodenum).
Also contains neuronal plexus = submucosal plexus(Meissner's) in most portions of GI tract.
3) Muscularis: has 2 layers of smooth muscle, an inner circular and an outer longitudinal with the myenteric plexus(Auerbach's) of nerves in between.
4) Serosa: is two layers, connective tissue internally, and has epithelium covering it, usually squamous epithelium, that corresponds to the visceral peritoneum.
3. Describe the innervation of the alimentary canal.
All enteric neurons in the plexus and support cells are derived from the neural crest. Thus they are intrinsic neurons(inside GI tract). The GI does still receive signals from extrinsic sources but only modify the activity.
Parasympathetic inputs from the Vagus nerves release acetylcholine, which increases motility in the GI tract.
Sympathetic inputs from the splanchnic nerves release norepinephrine, which relaxes the gut.
Scattered in epithelium are enteroendocrine cells (EC). They secrete mainly serotonin. The stretch (presence of food) on these EC cells cause the release of serotonin to stimulate peristalsis from the plexuses, and the release of gastrin and histamine to parietal cells to stimulate HCl production.
Myenteric plexus(Auerbach's Plexus): mostly motor, regulates peristalsis. Located between muscle layers in muscularis externa.
Submucosal plexus(Meissner’s plexus): Is secretory-motor. Release hormones and peptides. Innervate the mucosa and are located in the submucosa. Also communicate with the Myenteric plexus via hormone release to initiate peristalsis.
4. Describe the specializations of each region of the alimentary canal.
Esophagus
Has esophageal sero-mucus glands in the sub-mucosa( secrete mucous, pepsinogen, and lysozyme) that are responsive to HCl.
Also esophageal-cardiac mucous glands in the mucosa. Memory hint:Sero-Mucous(name),Sub-Mucosa(location),Serous-Mucous(secretion). CardiacMucosa secretes onlyMucous.
Upper region has skeletal muscle that phases out into smooth muscle on the way down, allowing voluntary control over swallowing.
Inner lining is Stratified Squamous Epithelium. Contains BOTH neural plexuses.
Cardiac Stomach
Contains no chief cells, but many surface lining cells. Has highly coiled glands with shallow gastric pits. Regenerative cells are found on the junction of the pit and gland, near the lumen. Glands are contained in the Lamina Propria of the mucosa. Stomach (all parts) DO NOT have the Submucosal Plexus, only the Myenteric Plexus.
Fundic/Body Stomach
Contains long, straight glands with short gastric pits. Chief cells in body release pepsinogen, renin, and gastric lipase. Many regenerative cells are found on the junction of the pit and gland, near the lumen.
Pyloric Stomach
Mainly mucous neck cells with very few chief cells. Contains branched, deep glands with deep gastric pits. Regenerative cells are found on the junction of the pit and gland.
Duodenum
Villi are broad, numerous, and tall. Few goblet cells. Brunner’s glands in the submucosa secrete alkaline mucous fluid to neutralize the acidic contents coming out of the stomach. Contains plicae circularis, villi, and microvilli to increase surface area. Has Crypts of Leieberkuhn in between villi with Paneth cells and regenerative cells at the bottom
Jejunum
Villi are narrower, shorter, and less dense than in the duodenum. Many goblet cells. Contains plicae circularis, villi, microvilli and crypts of Leieberkuhn inbetween villi.
Ileum
Villi are the shortest, narrowest and the fewest in number. Many goblet cells. Contains Peyer’s patches that are located opposite to where the mesentery attaches. Microfold cells are present to pickup and transport antigens to Peyer’s patches. Contains plicae circularis, villi, microvilli and crypts of Leieberkuhn inbetween villi.
Colon and Cecum
No villi or Paneth cells. Comprised of crypts of Leieberkuhn. Crypts contain goblet cells to protect large intestinal lumen. Muscularis externa is Teniae coli, which are constantly contracted to produce haustra and plicae semilunaris that form structural compartments.
Rectum
Crypts of Leieberkuhn are fewer but deeper. Increased number of goblet cells compared to the colon. At the rectal-anal junction, epithelium become stratified squamous non-keritinized and contains branched circumanal glands.
Anal Canal
Longtitudinal muscles in the rectum disappear to an elastich sheath. Contains the internal and external anal sphincter. Anal column forms perpendicular folds that increase flexibility. Pectinate line is where the rectal-anal junction changes epithelium from simple columnar to stratified squamous non-keratinized. Epithelium at the anal skin is stratified squamous keratinized.
Appendix
Contains Peyer’s patches on all sides, not just opposite to where the mesentery attaches.
5. Describe/list the functions of the alimentary canal by region and cell type.
Region
Cell Type
Function
Esophagus
Stratified squamous non-keratinized, sero-mucous and mucous glands, skeletal and smooth muscle
6. Describe the function of the specialized cells of the gut, e.g. digestive glands, gastric pits, enteroendocrine cells, paneth cells, mucus neck cells etc.
Myenteric/Auerbach’s Plexus
Derived from neural crest cells. Mostly motor nerves regulating peristalsis. Located between muscle layers in muscularis externa. Present in all parts of tract.
Submucosal (Meissner’s) Plexus
Derived from neural crest cells. Mainly secretory-motor, release hormones and peptides. Innervates the mucosa. Located in the submucosa. Absent in stomach.
Esophageal-cardiac Glands
Mucous glands in the esophagus at the pharynx and gastric junction.
Esophageal Sero-Mucous Glands
Serous-mucous glands in the submucosa of the esophagus. Secretes pepsinogen and lysozyme.
Gastric Pits
Invaginations of the stomach epithelium that lead to gastric glands at the bottom. Contain surface lining cells and regenerative cells.
Rugae
Folds in the mucosa and submucosa of the stomach.
Gastric Glands
Found in the lamina propria of the stomach and open into the gastric pits. Contains regenerative cells, mucous neck cells, parietal cells, chief cells, and enteroendocrine cells.
Parietal Cells
Stomach gastric gland cells that secrete hydrochloric acid and gastric intrinsic factor (for vitamin B12 metabolism).
Chief Cells
Stomach gastric gland cells that secrete pepsinogen, gastric lipase, and rennin.
Enteroendocrine Cells
Triangular-shaped cells with large nucleus. May contain granules. Found in glands and crypts.
Secretes serotonin, gastrin, histamine and other hormones. Also secretes glucagon and gastric inhibitory peptide in gastric glands to control parietal cells' HCl production.
Plicae Circularis
Large folds in the small intestine, including the mucosa and submucosa. Lined with Villi, which are lined with microvilli.
Villi
Projection of epithelium on small intestine. Contains individual smooth muscle strands(originating in musc. mucosa), blood vessels, and lymph vessels.
Paneth Cells
Found in the small intestine at the base of crypts. Secretes lysozyme, which breaks down bacterial walls. Exact function unknown, but diagnostic of small intestine.
Peyer’s Patches
Lymph organs found in the ileum and appendix.
Crypts of Lieberkuhn
Invaginations between villi in the small intestine and in the epithelium of the large intestine, containing regenerative cells and paneth cells(small intestine ONLY) at the bottom.
Brunner’s Glands
Found in the submucosa of the duodenum. Branched tubulo-alveolar glands that secrete alkaline mucous fluid to neutralize acidic chyme from the stomach.
Teniae coli
Discontinuous muscularis externa on the large intestine that are continually contracted, forming haustra and plicae semilunaris.
7. Describe the structural and functional regions of the esophagus.
Esophageal mucosa is stratified squamous nonkeratinized epithelium. The muscularis mucosae is discontinuous single layer of muscle. The lamina propria is dense irregular CT, has large amount of diffuse lymphoid tissue, arterioles and venuoles. The esophagus contains esophageal-cardiac glands located at junction of esophagus and stomach and at junction of esophagus and pharynx and sero-mucous glands along entire length of esophagus. The submucosa consists of dense fibroelastic CT, has esophageal glands and serous glands secreting pepsinogen and lysozyme. The muscularis externa of the upper region is all skeletal, the middle region transitions from skeletal to smooth and the lower region is all smooth muscle. The esophagus has adventitia connecting it to the diaphragm superiorly.
Esophagus, Stomach, and Intestines
1. Describe the overall plan of the alimentary canal.
1) esophagus- transport
2) stomach- mechanical disruption , absorption of water and alcohol
3) small intestine – chemical and mechanical digestion / absorption.
4) large intestine – absorb electrolytes (salts and water) and vitamins
5) rectum and anus – defecation
2. Describe the features of each layer of the alimentary canal.
1) Mucosa: 3 layers are always present in GI tube with varying thickness
- epithelium
- lamina propria- CT
- muscularis mucosae – thin layer of muscle
2) Submucosa: contains vessels, some nerves. Contains glands in 2 regions of GI (esophagus and duodenum).Also contains neuronal plexus = submucosal plexus(Meissner's) in most portions of GI tract.
3) Muscularis: has 2 layers of smooth muscle, an inner circular and an outer longitudinal with the myenteric plexus(Auerbach's) of nerves in between.
4) Serosa: is two layers, connective tissue internally, and has epithelium covering it, usually squamous epithelium, that corresponds to the visceral peritoneum.
3. Describe the innervation of the alimentary canal.
All enteric neurons in the plexus and support cells are derived from the neural crest. Thus they are intrinsic neurons(inside GI tract). The GI does still receive signals from extrinsic sources but only modify the activity.
Parasympathetic inputs from the Vagus nerves release acetylcholine, which increases motility in the GI tract.
Sympathetic inputs from the splanchnic nerves release norepinephrine, which relaxes the gut.
Scattered in epithelium are enteroendocrine cells (EC). They secrete mainly serotonin. The stretch (presence of food) on these EC cells cause the release of serotonin to stimulate peristalsis from the plexuses, and the release of gastrin and histamine to parietal cells to stimulate HCl production.
Myenteric plexus(Auerbach's Plexus): mostly motor, regulates peristalsis. Located between muscle layers in muscularis externa.
Submucosal plexus(Meissner’s plexus): Is secretory-motor. Release hormones and peptides. Innervate the mucosa and are located in the submucosa. Also communicate with the Myenteric plexus via hormone release to initiate peristalsis.
4. Describe the specializations of each region of the alimentary canal.
Esophagus
Has esophageal sero-mucus glands in the sub-mucosa( secrete mucous, pepsinogen, and lysozyme) that are responsive to HCl.
Also esophageal-cardiac mucous glands in the mucosa.
Memory hint: Sero-Mucous(name), Sub-Mucosa(location), Serous-Mucous(secretion). Cardiac Mucosa secretes only Mucous.
Upper region has skeletal muscle that phases out into smooth muscle on the way down, allowing voluntary control over swallowing.
Inner lining is Stratified Squamous Epithelium. Contains BOTH neural plexuses.
Cardiac Stomach
Contains no chief cells, but many surface lining cells. Has highly coiled glands with shallow gastric pits. Regenerative cells are found on the junction of the pit and gland, near the lumen. Glands are contained in the Lamina Propria of the mucosa. Stomach (all parts) DO NOT have the Submucosal Plexus, only the Myenteric Plexus.
Fundic/Body Stomach
Contains long, straight glands with short gastric pits. Chief cells in body release pepsinogen, renin, and gastric lipase. Many regenerative cells are found on the junction of the pit and gland, near the lumen.
Pyloric Stomach
Mainly mucous neck cells with very few chief cells. Contains branched, deep glands with deep gastric pits. Regenerative cells are found on the junction of the pit and gland.
Duodenum
Villi are broad, numerous, and tall. Few goblet cells. Brunner’s glands in the submucosa secrete alkaline mucous fluid to neutralize the acidic contents coming out of the stomach. Contains plicae circularis, villi, and microvilli to increase surface area. Has Crypts of Leieberkuhn in between villi with Paneth cells and regenerative cells at the bottom
Jejunum
Villi are narrower, shorter, and less dense than in the duodenum. Many goblet cells. Contains plicae circularis, villi, microvilli and crypts of Leieberkuhn inbetween villi.
Ileum
Villi are the shortest, narrowest and the fewest in number. Many goblet cells. Contains Peyer’s patches that are located opposite to where the mesentery attaches. Microfold cells are present to pickup and transport antigens to Peyer’s patches. Contains plicae circularis, villi, microvilli and crypts of Leieberkuhn inbetween villi.
Colon and Cecum
No villi or Paneth cells. Comprised of crypts of Leieberkuhn. Crypts contain goblet cells to protect large intestinal lumen. Muscularis externa is Teniae coli, which are constantly contracted to produce haustra and plicae semilunaris that form structural compartments.
Rectum
Crypts of Leieberkuhn are fewer but deeper. Increased number of goblet cells compared to the colon. At the rectal-anal junction, epithelium become stratified squamous non-keritinized and contains branched circumanal glands.
Anal Canal
Longtitudinal muscles in the rectum disappear to an elastich sheath. Contains the internal and external anal sphincter. Anal column forms perpendicular folds that increase flexibility. Pectinate line is where the rectal-anal junction changes epithelium from simple columnar to stratified squamous non-keratinized. Epithelium at the anal skin is stratified squamous keratinized.
Appendix
Contains Peyer’s patches on all sides, not just opposite to where the mesentery attaches.
5. Describe/list the functions of the alimentary canal by region and cell type.
6. Describe the function of the specialized cells of the gut, e.g. digestive glands, gastric pits, enteroendocrine cells, paneth cells, mucus neck cells etc.
Myenteric/Auerbach’s Plexus
Derived from neural crest cells. Mostly motor nerves regulating peristalsis. Located between muscle layers in muscularis externa. Present in all parts of tract.
Submucosal (Meissner’s) Plexus
Derived from neural crest cells. Mainly secretory-motor, release hormones and peptides. Innervates the mucosa. Located in the submucosa. Absent in stomach.
Esophageal-cardiac Glands
Mucous glands in the esophagus at the pharynx and gastric junction.
Esophageal Sero-Mucous Glands
Serous-mucous glands in the submucosa of the esophagus. Secretes pepsinogen and lysozyme.
Gastric Pits
Invaginations of the stomach epithelium that lead to gastric glands at the bottom. Contain surface lining cells and regenerative cells.
Rugae
Folds in the mucosa and submucosa of the stomach.
Gastric Glands
Found in the lamina propria of the stomach and open into the gastric pits. Contains regenerative cells, mucous neck cells, parietal cells, chief cells, and enteroendocrine cells.
Parietal Cells
Stomach gastric gland cells that secrete hydrochloric acid and gastric intrinsic factor (for vitamin B12 metabolism).
Chief Cells
Stomach gastric gland cells that secrete pepsinogen, gastric lipase, and rennin.
Enteroendocrine Cells
Triangular-shaped cells with large nucleus. May contain granules. Found in glands and crypts.
Secretes serotonin, gastrin, histamine and other hormones. Also secretes glucagon and gastric inhibitory peptide in gastric glands to control parietal cells' HCl production.
Plicae Circularis
Large folds in the small intestine, including the mucosa and submucosa. Lined with Villi, which are lined with microvilli.
Villi
Projection of epithelium on small intestine. Contains individual smooth muscle strands(originating in musc. mucosa), blood vessels, and lymph vessels.
Paneth Cells
Found in the small intestine at the base of crypts. Secretes lysozyme, which breaks down bacterial walls. Exact function unknown, but diagnostic of small intestine.
Peyer’s Patches
Lymph organs found in the ileum and appendix.
Crypts of Lieberkuhn
Invaginations between villi in the small intestine and in the epithelium of the large intestine, containing regenerative cells and paneth cells(small intestine ONLY) at the bottom.
Brunner’s Glands
Found in the submucosa of the duodenum. Branched tubulo-alveolar glands that secrete alkaline mucous fluid to neutralize acidic chyme from the stomach.
Teniae coli
Discontinuous muscularis externa on the large intestine that are continually contracted, forming haustra and plicae semilunaris.
7. Describe the structural and functional regions of the esophagus.
Esophageal mucosa is stratified squamous nonkeratinized epithelium. The muscularis mucosae is discontinuous single layer of muscle. The lamina propria is dense irregular CT, has large amount of diffuse lymphoid tissue, arterioles and venuoles. The esophagus contains esophageal-cardiac glands located at junction of esophagus and stomach and at junction of esophagus and pharynx and sero-mucous glands along entire length of esophagus. The submucosa consists of dense fibroelastic CT, has esophageal glands and serous glands secreting pepsinogen and lysozyme. The muscularis externa of the upper region is all skeletal, the middle region transitions from skeletal to smooth and the lower region is all smooth muscle. The esophagus has adventitia connecting it to the diaphragm superiorly.